Originally posted by coolgeek84:
Good question, I also always wonder about this. Human ear can only hear frequencies of 20Hz to 20KHz. Then whats the purpose of headphones advertising below 20Hz and above 20Khz?
Do they mean that some humans have ultra powerful hearing senses?

And what "household" items can produce noises at this frequencies? Very hard to find out.. But if any of you come across this kinda info please share..
use freeware
audacity is a program that record soud straight from soundcard
there a feature that lets u generate a tone
u can adjust it to the hz u like
for low frequency, please make sure ur subwoofer can take it